The present invention relates to a method and apparatus for measuring the shape of a specimen by using the signals emitted from the specimen as a result of exposure of the specimen to electromagnetic wave or electrically charged particles and a method of estimating the features of a semiconductor device from the value or changes in the value of shape parameters acquired by measuring or a method of estimating or monitoring the state of the semiconductor production process.
For forming a line pattern on a semiconductor wafer, the method of coating the semiconductor wafer with a coating material called resist, covering the resist with a mask on which a line pattern is formed, irradiating the masked semiconductor wafer with a visible ray, ultraviolet ray or electronic beam for exposing the resist to the rays is adopted. Due to changes in the tilt angle and the shape of the sloping part of the line pattern thus acquired depending on the density and focusing of the visible ray, ultraviolet ray or electronic beams applied, in order to form a high-precision line pattern, it is necessary to measure and examine the three-dimensional shape of the pattern. For this examination, the sectional shape can be measured precisely by cutting the wafer and by measuring the sectional shape. However, this process requires manpower and costs. For this reason, a non-destructive and noncontact method of measuring the sectional shape of patterns by means of scanning electron microscopy (hereinafter referred to as “SEM”) is proposed.
As a method of acquiring tilt images where in the object of measurement is observed from any freely chosen tilt angle by means of SEM, there is for example a method of deflecting the electronic beams applied by the electro-optical system, and tilting the irradiation angle of the electronic beams to pick up tilt images as shown in the Japanese Patent Application Laid Open 2000-348658. And as a method for measuring the sectional shape of the object, there is for example a method of measuring sectional shape combining the shape from shading method using the tilt images as shown in the Japanese Patent Application Laid Open 2003-315029 and the Japanese Patent Application Laid Open 2000-146558 and the stereo-matching method. This method detects the characteristic points of the signal wave form detected by the secondary electron detector of SEM, measure the absolute value of the height of the section by stereo matching of the characteristic points, and calculates the shape between characteristic points based on the shape from shading method.
And the Japanese Patent Application Laid Open 1993-181980 discloses a method of detecting edges from two-dimensional luminance image data, calculating an index value showing the smoothness of the surface of the object of measurement from the edges, and restoring the three-dimensional shape of the object of measurement by using this index value as a means of restoring a correct three-dimensional shape in response to abrupt changes in the surface of the object of measurement.
Relating to the two-dimensional or three-dimensional shape of semiconductor patterns measured by any freely chosen two-dimensional or three-dimensional shape measurement method, the present invention relates to a method of reforming a two-dimensional or three-dimensional shape of a higher precision by correcting the measured points for which a high precision could not be achieved only by the freely chosen two-dimensional or three-dimensional shape measurement method based on the image feature value (hereinafter referred as “shape index value”) related with the two-dimensional or three-dimensional shape.
In the past, it was difficult to easily correlate two-dimensional or three dimensional shapes with shape index values. For example, according to the method described in the Japanese Patent Application Laid Open 1993-181980, shapes were corrected by correlating the parameter of the shape calculating equation proper for the measurement method used for two-dimensional or three-dimensional shapes and the index value and by adjusting the parameters mentioned above. However, the correction method was not for the general use and it was often difficult to apply the method to any two-dimensional or three-dimensional shape measuring method. For example, it could not be applied to measurement methods having no parameters to control shape at the time of calculating shapes such as scanning probe microscope (hereinafter referred to as “SPM”). And due to the fact that the freedom of varying shape by correction depended on the model equation used in the calculation of shape, it was not suitable for objects of correction having a wide room for the variation of shape.
Also in the past it was difficult to visualize and easily carry out a learning operation. For example, when a shape is to be corrected, a learning step is required for expressing in advance the relationship with parameters expressing the magnitude and the degree of correction of the shape index value (for example the degree of rounding the shape of corners) in a look-up table or any equation. However, it was difficult for any operator not having sufficient knowledge relating to algorithm inside to judge what kind of parameters should be supplied and whether a sufficient learning had been made, and the learning operation was generally a complicated and difficult operation.